Re: [ft] Glyph hinting problem with TT hinter

[Rogier van Dalen]

On 3/30/06, Werner LEMBERG <address@hidden> wrote:
> > > The size is 20 pixels.  This can be easily seen in the ftview
> > > demo. Set resolution 72 dpi, size 20 points, font Arial Unicode MS
> > > Check the letter W. The middle is asymmetric which is noticeable
> > > when there are several W in a row
> >
> > Indeed, this is a really noticeable artifact.  Unfortunately, I
> > don't have Arial Unicode MS, and my other Arial fonts don't exhibit
> > this problem.
>
> Meanwhile I've found this font on my harddisk.  Attached is the
> problematic glyph which I've extracted -- it will take some time until
> I've analyzed this issue.  Maybe someone else want to play with it...

Werner, I thought you always CC-ed me when things like these came up!
;-) This time I noticed this thread. I see the very same asymmetry on
my rasterizer.
Point 25 is the problematic point. I've calculated it all; Microsoft
rounds the x-coordinate 895.455782 up to 896 (14.0) in an interpolate
instruction. It is then rounded to half a pixel, to 14.5 according to
the MS interpreter, to 13.5 according to FreeType's and mine. A delta
instruction then moves it left to 13.5 (12.5). To conclude, the MS
rasterizer does faulty rounding here, and a delta instruction could
have been spared if they had implemented it properly.

A related point: do you keep some registry of these discrepancies?
We've seen a couple now. At some point duplicate bug reports will
occur. At some point someone might want to adapt the FreeType
interpreter to mimic all MS rounding errors.

Regards,
Rogier